Thanks for the link. But E-Signature and E-Records is used in Manufacturing Cloud, Inventory Management Cloud, and Quality Inspection. The Digital Signature requirement is for Contract documents, PO print and other documents like Remittance advice sent to suppliers etc.,

For Digital signatures, are you looking at leveraging the out of the box integration with DocuSign? If yes, then Purchasing documents canbe digitally signed via docusign integration. Please refer below document.